WASHINGTON — Rival militant organizations on both sides of the Afghanistan-Pakistan border have increasingly been teaming up in deadly raids, in what military and intelligence officials say is the insurgents’ latest attempt to regain the initiative after months of withering attacks from U.S. and allied forces.

New intelligence assessments from the region assert that insurgent factions now are setting aside their historic rivalries to behave like “a syndicate,” joining forces in ways not seen before. After one recent attack on a remote base in eastern Afghanistan, a check of the dead insurgents found evidence that the fighters were from three factions, military officials said.

In the past, these insurgent groups have been seen as sharing ideology and inspiration, but less often plans for specific missions.

Now, the intelligence assessments offer evidence of a worrisome new trend in which extremist commanders and their insurgent organizations are coordinating attacks and even combining their foot soldiers into patchwork patrols sent to carry out specific raids.

The change reveals the resilience and flexibility of the militant groups. But at the same time, officials say, the unusual and expanding alliances suggest that the factions are feeling new military pressure. U.S. and NATO officials say these decisions by insurgent leaders are the result of operations by U.S., Afghan and allied forces on one side of the border, and by the Pakistani military — and U.S. drone strikes — on the other.

U.S. commanders recently have been seeking even more latitude to operate freely along the porous border, including inside Pakistan, and have consistently warned that whatever gains they have made in the past few months are fragile. One official said it was “a wake-up call” to find evidence, after the attack on the forward operating base, that the fighters were partisans from three factions with long histories of feuding: the Quetta Shura Taliban of Mullah Muhammad Omar; the network commanded by the Haqqani family; and fighters loyal to the Hekmatyar clan.

These extremist groups have begun granting one another safe passage through their areas of control in Afghanistan and Pakistan, sharing new recruits and coordinating their propaganda responses to U.S. and allied actions on the ground, officials said.

U.S. military officials sought to cast these recent developments as a reaction to changes in the U.S. and allied strategies in the past year, including aggressive military offensives against the insurgents coupled with attempts to provide visible and reliable protection to the local Afghan population.

During the past 90 days, signs of this new and advanced syndication among insurgent groups have been especially evident in two provinces of eastern Afghanistan, Kunar and Paktika.

"There is a general recognition that we don't need these military-style weapons in New Zealand, so it's very easy to win cross-party support for this," said Mark Mitchell, who was defense minister in the previous, center-right government and who supports the ban initiated by the center-left-led Labour Party.